Forming rolls

ABSTRACT

The invention relates to a method for producing gear forming rolls. Gears can be manufactured by rolling and squeezing blanks between forming rolls, but in practice the exact shape of the teeth in the rolls is not given to the gear being rolled. Thus, to produce the desired tooth profile on the finished rolled gear, the tooth profile of the forming roll must be modified. The invention provides a method for producing forming rolls for roll forming gears, which comprises rolling an accurate finished gear against a soft blank, and thereafter using the shaped blank in the preparation of the forming roll. The method of the invention avoids the time consuming and expensive trial and error methods of the prior art.

United States Patent 1191 Connell Nov. 12, 1974 [54] FORMING ROLLS FOREIGN PATENTS OR APPLICATIONS [75] lnvemori g z s 184.237 7/1966 U.S.S.R 72/102 e ten am, ng an [73] Assignee: Formflo Limited, Gl t hi Primary ExaminerLowell A. Larson En 1 d Attorney, Agent, or Firm-Pollock, Philpitt & Vande g n i S d an e [22] Filed: Nov. 22, 1972 I [21] Appl. No.: 308,871 [57 ABSTRACT The invention relates to a method for producing gear [30] Foreign Application Priority Data forming rolls. Gearscan be manufactured by rolling N 24 1971 G 54644 7] and squeezing blanks between forming rolls, but 1n rea n practice the exact shape of the teeth in the rolls is not given to the gear being rolled. Thus, to produce the, 72/68 z gi desired tooth profile on the finished rolled gear, the- [58] Fieid 108v 366 tooth profile of the forming roll must be modified. The 9 invention provides a method for producing forming rolls for roll forming gears, which comprises rolling an accurate finished gear against a soft blank, and there- [56] References Cited after using the shaped blank in the preparation of the UNITED STATES PATENTS forming roll. The method of the invention avoids the 1,712,095 5/1929 Schurr 29/1592 time consuming and expensive trial and error methods 3,362,059 l/l968 DiPonio et. al 29/1592 f the an 3,631,703 1/1972 Bregi et al. 29/1592 p 3,720,989 3 1973 Ramond 29 1592 10 Chums, 2 Drawmg Figures 1 FORMING RoLLs This invention relates to the manufacture of forming rolls which can be used in the roll forming of gears.

Gears can bemanufactured from a gear blank by rolling and squeezing the blank between two rotating forming rolls. ln practice, however, the exact shape of the teeth in the rolls is not given to the gear being rolled. For example, when the forming rolls have involute teeth, hollow profiles are produced in the gear tooth flanks and protruberances of the gear teeth tips tend to occur.

In order to produce the desired tooth profile on the finished rolled gear, the tooth profile of the forming roll must therefore be modified. This is achieved by trial and error and requires a considerable number of roll regrinds before an acceptable roll is produced. This is both time consuming and expensive andis necessary for each forming roll for each type of gear to be formed.

The invention has been made with these points in mind.

According to the invention forming rolls for roll forming gears are prepared by rolling an accurate finished reference gear against a relatively soft blank so giving that blank the shape required of a forming roll for roll forming gears to the shape of the reference gear, and thereafter using that shaped blank in the preparation of the forming roll.

The method of the invention enables forming rolls to be produced having that particular tooth flank profile which will give the accurate desired Profile to rolled gears without the numerous and onerous steps previously required.

The accurate finished reference gear which is used to shape the soft blank can be manufactured conventionally by machining and should be sufficiently hard to shape the relatively soft blank without deforming it. This gear can then be roll formed against the relatively soft blank, which may either be already partially shaped or may be a plain-cylinder, using a suitable roll forming machine.

The relatively soft shaped'flank is then used in the preparation of the required forming roll.-

If the relatively soft blank has been made from a suitable hardenable material such as steel, then one can simply harden the blank, e.g. by suitable heat treatment to give the formingroll, provided, of course, the heat treatment will not distort the shapedblank.

Alternatively, one can take suitable measurements from the shaped blank and grind a hardened cylinder to give the required forming roll. The forming roll thus ground to shape can be given an identical shape and size to those of the shaped blank. However, one can often achieve higher accuracy by modifying the profile measured from the shaped blank in comparison with a theoretically calculated profile so as to improve still further the conformity of gears rolled by the forming rolls to the ideal final desired profile of the initial. reference gear.

A particularly useful tooth flank profile which can be produced in gears rolled with the forming rolls of the invention is the involute form. Preferably the relatively soft blank is partially preformed with a true involute form on the drive and coast sides of the teeth and this form is blended with a full cap radius so as to achieve tip clearance during the roll forming. Then this shape is then modified by rolling against the reference-gear so that the forming roll reproduced from this produces accurate rolled gears.

To obtain a partially preformed relatively soft blank, the base diameter is calculated from the ratio of the number of teeth on the partially preformed blank to the number of teeth on the gear blank. This ratio can be calculated or obtained from a pictorial examination.

After consideration of the parameters of the required involute profile on the rolled gears the rolling pressure angle of the gear blank can be calculated. Hence important dimensions such as the preformed blank to gear blank'centre distance, rolling pitch radius and length of line of action can also be calculated.

By laying off the various important datums of the involute profile required on the gear blank along the line of action and then considering the manner of rolling intended, the various radii at the mating points along the involute profile of the preformed blank can be calculated.

By the application of conventional gear-theory the rolled gear tooth thickness at the rolling pitch radius can be calculated and this is used to calculate the required partially preformed blank tooth thickness at the rolling pitch radius and hence the pitch circle of .the partially preformed blank. The various radii mentioned above can now be converted to angles of roll along an involute curve generated from the base diameter of the partiallypreformed blank.

Having obtained a soft blank tooth thickness at the rolling pitch radius, the blank tooth thickness at various roll angles along the involute can be calculated and thus allow close examination of-the blank tooth form, particularly near the root and the tip. 7 f

' The various dimensions thus obtained can be utilized, in conjunction with the relevant part dimensions to calculate the partially preformed blank outer diameter,

root diameter, blank tooth tip radius and blank tooth radius. An initial relatively soft blank can thus be obtained having a true involute form on the drive and coast sides and these are blended with a full cap radius so as to achieve tip clearance during the roll forming.

gear can be given, and the rolling completed on reaching the correct gear centre distance.

On reaching the predetermined gear centre distance all, ora selected number, of teeth on the relatively soft blanks are measured with regard to form profile on both the drive and coast. sides. The purpose of checking a number of teeth in the soft blanks is to obtain the average form of the profile, as there may be some minute variations due to inaccuracies in the measuring equipment and also the reference gear.

The modified involute profile on the blank tooth flanks are now recorded and forming rolls can be manufactured with identical profiles.

To improve rolling accuracy 'still the final forming rolls may have to be given a profile modified with respect to that formed in the soft blank. This can be achieved by calculating the theoretical shape of the required shaped blank profile which can further, however,

be carried out, for example, by drawing a graph of the sliding velocity relative the reference circle at various points of the roll profile. The sense of the graph will then show the sense in which the modified involute form must be applied to each side of the teeth on the forming roll to give an excellent rolled gear. Thus the degree of modification can be obtained fromthe step of rolling the accurately finished reference gear against the soft blank while the sense of modification on the drive and coast sides of the teeth can be determined from studying the velocity graph, and the forming roll ground to shape accordingly.

Alternatively providing the shaped blanks are of a suitable material which does not substantially distort on heat treatment they can be heat treated directly after rolling with the reference gear. The latter method has the advantage that it avoids any further grinding which is necessary when the forming rolls dies are made by grinding blanks to the profile obtained during the profile modification step.

The profile modification technique can be applied to profiles such as for example, helical and spur lead gears as well as to involute profiles. The process can also be carried out warm or hot by heating the relatively soft blanks prior to rolling.

The roll forming of the relatively soft blank can be effected by rotatably mounting a pair of blanks one in each of a pair of opposed heads between which the reference gear is rotatably held and then urging the two blanks in towards one another diametrically of the reference gear while rotating the blanks to effect the rolling. This technique can also be used where only one soft blank is used, and is effected by rotatably mounting one blank in one head suitably opposed to a rotatably held reference gear. The blank is then urged diametrically towards the reference gear while rotating the blank and reference gear to effect rolling.

The rolling should be continued until the rolling depth reaches the correct calculated gear centre distance.

The invention will now be described by way of example with reference to the accompanying diagrammatic drawings, in which:

FIG. 1 is a diagram showing the desired tooth profile and the tooth profile which results when a gear is rolled using a forming roll with a involute shaped profile; and

FIG. 2 is a diagram showing the roll forming of a roll blank according to the invention.

In FIG. 1 the gear tooth profile 1 having an involute form 3 is the profile which is required in the gears roll formed by the forming rolls produced by the method of the invention.

The tooth profile 2 is the profile produced in a gear by rolling an unmodified forming roll having involute teeth against the gear. As shown the profile comprises.

blanks 19. The reference gear 11 is mounted on a mandrel 13 which is supported at opposite ends in bearins (not shown) while the rolls are rotatably mounted in the arms 8 of the sliding yokes 9. These yokes are slidably mounted so as to be moveable towards and away from one another.

The surfaces 12 of the preformed blanks 19 are manufactured to a hobbed or shaped condition and are in an unheat treated state. The mandrel 13 fits within the reference gear 11 and maintains a plain cylindrical inner facing on the gear during rolling.

The yokes 9 carrying the blanks 19 are slidably mounted so that they can be advanced to effect the modification of the die tooth profile. The yokes are caused to slide by means of a hydraulic ram 21. Pressurized hydraulic fluid is supplied through the line 29 into the ram to operate the piston 25 and subsequently cause the yokes 9 to advance.

Sufficient metal is left on the flanks of the blanks teeth in order that the modified involute form which will be produced by rolling against the reference gear 11 can be given.

Rolling is effected by passing hydraulic fluid through .the line 29 which operates the piston 25 causing the yolks 9 to advance, and is completed when the predetermined gear centre distance is reached.

A selected number of teeth on the soft blanks 19 are then measured with regard to form profile on both the drive and coast sides to obtain the average form of the profile.

If the shaped blanks are of a suitable hardenable material such as steel they can be heat treated to provide the rolling die.

Alternatively,measurements can be taken from the modified involute profile on the shaped blank, and dies can be manufactured with identical profiles. To improve the profiles on the manufactured dies the profiles can be modified in comparison with a theoretically cal culated profile as hereinbefore described.

The invention thus has the advantage that it provides an inexpensive and relatively quick method for developing and producing a forming roll for roll forming gears.

What I claim is:

l. A method of preparing a forming roll for use in preparing gears by roll forming workpieces comprising I the steps of:

2. A method according to claim 1 in which said blank is made of a material which can be heat hardened substantially without distortion.

3. A method according to claim 1 in which said reference gear has teeth with drive and coast sides and has a true involute form on said drive andcoast sides.

4. A method according to claim I further comprising the step of preforming said relatively soft blank to provide on it teeth having drive and coast sides and a tip, said drive and coast sides of said teeth having a true involute form, said involute forms blending to a full cap radius at said tip.

5. A method of preparing a forming roll for use in preparing gears by roll forming workpieces comprising the steps of:

a. preparing a reference gear by machining operations not including rolling, having teeth whose profile corresponds accurately to the desired profile of said gears,

b. rolling said reference gear against a blank of mate rial softer than the material of said reference gear to shape in said blank teeth having a modified profile,

c. determining the average shape of the modified profile of said teeth'in said blank, and

d. grinding in a hardened die blank teeth of said average shape of sald modified profile to give a forming roll which, when used with said workpieces provides teeth corresponding accurately to said desired profile.

6. A method according to claim 5 in which said reference gear has teeth with drive and coast sides and has a true involute form on said drive and coast sides.

7. A method according to claim 5 further comprising the step of preforming said relatively soft blank to provide on it teeth having drive and coast sides and a tip, said drive and coast sides of said teeth having a true involute form, said involute forms blending to a full cap radius at said tip. v

8. A method of preparing a forming roll for use in preparing gears by roll forming workpieces comprising the steps of:

a. preparing a reference gear by machining operations not includingrolling, having teeth whose profile corresponds accurately to the desired profile of said gears,

b. rolling said reference gear against a blank of material softer than the material of said reference gear to shape in said blank teeth having a modified profile.

c. determining the average shape of the modified profile of the said teeth in sald blank,

d. calculating the theoretical shape which the teeth of the blank should have to reproduce said desired profile in roll formed gears, and

e. grinding in a hardened die blank teeth whose profile differs from said desired profile of said reference gear at each point along the profile of the teeth in an amount determined from said average shape of said modified profile of said teeth in said blank and in the sense of increased or decreased tooth width determined by the difference of the theoretical shape from said desired profile.

9. A method according to claim 8 further comprising the step of obtaining said theoretically calculated profile by drawing a graph of the sliding velocity relative the reference circle at various points of the roll profile.

10. A method according to claim 8 further comprising the step of preforming said relatively soft blank to provide on it teeth having drive and coast sides and a tip, said drive and coast sides of said teeth having a true involute form, said involute forms blending to a full cap radius at said tip. 

1. A method of preparing a forming roll for use in preparing gears by roll forming workpieces comprising the steps of: a. preparing a reference gear by machining operations not including rolling, having teeth whose profile corresponds accurately to the desired profile of said gears, b. rolling said reference gear against a blank of material softer than the material of said reference gear to shape in saId blank teeth having a modified profile, and c. hardening said blank to give said forming roll which, when used to roll form said gears from said workpieces, will shape in said workpieces teeth corresponding accurately to saId desired profile.
 2. A method according to claim 1 in which said blank is made of a material which can be heat hardened substantially without distortion.
 3. A method according to claim 1 in which said reference gear has teeth with drive and coast sides and has a true involute form on said drive and coast sides.
 4. A method according to claim 1 further comprising the step of preforming said relatively soft blank to provide on it teeth having drive and coast sides and a tip, said drive and coast sides of said teeth having a true involute form, said involute forms blending to a full cap radius at said tip.
 5. A method of preparing a forming roll for use in preparing gears by roll forming workpieces comprising the steps of: a. preparing a reference gear by machining operations not including rolling, having teeth whose profile corresponds accurately to the desired profile of said gears, b. rolling said reference gear against a blank of material softer than the material of said reference gear to shape in said blank teeth having a modified profile, c. determining the average shape of the modified profile of said teeth in said blank, and d. grinding in a hardened die blank teeth of said average shape of saId modified profile to give a forming roll which, when used with said workpieces provides teeth corresponding accurately to said desired profile.
 6. A method according to claim 5 in which said reference gear has teeth with drive and coast sides and has a true involute form on said drive and coast sides.
 7. A method according to claim 5 further comprising the step of preforming said relatively soft blank to provide on it teeth having drive and coast sides and a tip, said drive and coast sides of said teeth having a true involute form, said involute forms blending to a full cap radius at said tip.
 8. A method of preparing a forming roll for use in preparing gears by roll forming workpieces comprising the steps of: a. preparing a reference gear by machining operations not including rolling, having teeth whose profile corresponds accurately to the desired profile of said gears, b. rolling said reference gear against a blank of material softer than the material of said reference gear to shape in said blank teeth having a modified profile. c. determining the average shape of the modified profile of the said teeth in saId blank, d. calculating the theoretical shape which the teeth of the blank should have to reproduce said desired profile in roll formed gears, and e. grinding in a hardened die blank teeth whose profile differs from said desired profile of said reference gear at each point along the profile of the teeth in an amount determined from said average shape of said modified profile of said teeth in said blank and in the sense of increased or decreased tooth width determined by the difference of the theoretical shape from said desired profile.
 9. A method according to claim 8 further comprising the step of obtaining said theoretically calculated profile by drawing a graph of the sliding velocity relative the reference circle at various points of the roll profile.
 10. A method according to claim 8 further comprising the step of preforming said relatively soft blank to provide on it teeth having drive and coast sides and a tip, said drive and coast sides of said teeth having a true involute form, said involute forms blending to a full cap radius at said tip. 